Question:
Answer:
To those who lack faith there is no miracle that will convince them.
The Church always wishes to be cautious when officially recognizing a miracle. The Church attempts to first rule out any natural explanation. If a particular medical condition is known to have spontaneous remission in a good number of cases then such a healing probably would not be recognized by the Church as a miracle.
The Church does use medical experts to evaluate claims of miracles. The Church simply asks these experts to determine what the natural explanation would be, if there is one. They establish the exact diagnosis of the illness, prognosis, treatment and end result. In order to be considered as a possible miracle, the medical experts must determine that the cure was rapid, complete, lasting, and inexplicable by current medical and scientific knowledge.
After a claimed miracle passes the medical test, it must then pass a theological test. The theologians try to ascertain whether it is reasonable to connect the medically inexplicable cure to the particular saint or devotion.
If a claimed miracle passes both of these inquiries, the results of both reports are given to the Pope who then makes his own decision.
If spontaneous remission for a particular condition is so rare as to not be a likely explanation and the remission coincided with a particular devotion to a saint then it would seem much more reasonable, for a person of faith, to assume a miracle than to assume an odd coincidence of astronomical probability.
For further reading: Divinus Perfectionis Magister